1. Field of the Invention
The present invention relates to a variable capacitor, and more particularly, to a variable capacitor in which the effective opposing area between a stator and a rotor is varied by the rotation of the stator with respect to the rotor, whereby the electrostatic capacitance is adjusted.
2. Description of the Related Art
In one conventional variable capacitor, the effective opposing area between the stator and the rotor is varied by the rotation of the rotor with respect to the stator, whereby the capacity is adjusted.
In a variable capacitor of the type described above, a driver member is constructed to be rotated by a tool such as a screwdriver or other suitable tool and rotate a rotor, caused by the rotation transmitted to the rotor.
In many of the above-described conventional variable capacitors, the rotor is stably contacted with a stator while the rotor is rotated, such that an adjusted electrostatic capacitance is maintained constant. Moreover, in many cases, a spring member is disposed between the above-mentioned driver member and the rotor.
The driver and spring members as described above are provided as separate members and are joined to each other by welding, crimping, or other suitable joining method, as described in, e.g., Japanese Unexamined Patent Application Publication No. 3-141628 or Japanese Unexamined Patent Application Publication No. 8-306587.
These publications disclose a spring member provided with spring function portions extending radially in four directions from the center axial line of the driver member.
However, the above-described conventional variable capacitors have problems, especially with respect to the driver members and the spring members.
First, it is necessary to configure the driver member and the spring member as separate components. Thus, the number of components is increased, and moreover, a process for integrating these two members is required.
Furthermore, only a spring function portion having a length smaller than the radius of the driver member can be disposed in the driver member. Thus, the width is relatively small. Accordingly, the elastic range is narrow, and the spring property is often insufficient. If an overload is applied to the spring function portion, the portion plastically deforms. Moreover, the spring property of the spring function portion extending in each of the four directions varies.
As a result, the contact of the rotor with the stator is unstable. Therefore, the adjusted electrostatic capacitance is unstable, and moreover, torque generated by the rotation-operation of the rotor is not constant.
To overcome the above-described problems with the prior art, preferred embodiments of the present invention provide a variable capacitor having a stator fixedly disposed and defining a stator electrode, a rotor disposed rotatably in contact with the stator and having a rotor electrode opposed to the stator electrode via a dielectric member, an electrically conductive driver member which is rotation-operated so as to rotate the rotor and including an engagement portion engaged with the rotor such that the rotation is transmitted to the rotor, and a driver groove provided to perform the rotation-operation, an electrically conductive center shaft rotatably supporting the rotor and the driver member and being electrically connected to the driver member, a stator terminal electrically connected to the stator electrode, and a rotor terminal electrically connected to the center shaft.
To solve the above-described technical problems, the variable capacitor of various preferred embodiments of the present invention includes the following features.
The driver member preferably includes one metal sheet in which a head having a driver groove positioned therein and the engagement portion are integrally provided together with the spring function portion pressure-contacted with the rotor to elastically press the rotor against the stator.
Furthermore, the spring function portion includes a plate portion extending from one end of the head, which is bent from the one end of the head and is elongated, passing the center shaft. This plate portion functions as a pressure-contact component for the rotor.
Preferably, the spring function portion includes a first plate portion extending from one end of the head, which is bent in a first bending portion, and extending along the underside of the head, passing the center shaft, and a second plate portion extending from the end of the first plate portion, which is bent in a second bending portion, and extending along the underside of the first plate portion, passing the center shaft, the second plate portion functioning as a pressure-contact component for the rotor.
Also preferably, a gap is provided between the first plate portion and the second plate portion.
The spring function portion further includes a support portion provided by bending the end portion of the second plate portion in a direction such that the end portion approaches the underside of the head.
Preferably, the second plate portion includes a projected portion provided in the pressure-contact component for the rotor.
Also preferably, the first bending portion includes a through-hole provided in the approximate center in the width direction thereof.
In addition, preferably, the spring function portion is further provided with a pair of auxiliary pressure-contact portions, each extending from the sides of the first plate portion to approach the upper side of the rotor.
Preferably, the rotor includes a pair of engagement walls extending substantially vertically and facing in the same direction, the center shaft member is arranged between the engagement walls, and the engagement portions of the driver member are in contact with the pair of the engagement walls, respectively.
The rotor is configured in the shape of a substantially semi-circular sheet, of which the underside defines a substantially semi-circular rotor electrode. In the rotor having such a configuration, the linear portions of the substantially semi-circular shape of the rotor define the pair of the engagement walls.
Also preferably, the engagement portions are configured to extend from the second plate portions.
The cut end-surfaces of the engagement portions are engaged with the pair of the engagement walls. Preferably, bent ends having a bent shape are provided in the free ends of the engagement portions, respectively, and the bent ends of the engagement portions are engaged with the pair of the engagement walls.
Moreover, preferably, the engagement portions are engaged with the outermost ends of a pair of the engagement walls.
In the variable capacitor of a preferred embodiment of the present invention, the head provided in the driver member is preferably dish-shaped, and preferably, the driver groove is provided in the side surface of the head. More preferably, the driver groove is configured such that it does not extend to the bottom of the dish-shaped head.
Also preferably, the center shaft and the rotor terminal are preferably integral with each other.
In the above case, preferably, the variable capacitor is further provided with a case made of resin, the case having a concavity fixedly accommodating the stator, and rotatably accommodating the rotor and the driver member, and being formed by insert-molding with the stator terminal and the rotor terminal.
Also preferably, the stator is made of a dielectric having the stator electrode provided on the underside thereof, the rotor is electrically conductive and is disposed on the upper side of the stator rotatably in contact with the upper side of the stator, and the rotor electrode is provided on the underside of the rotor to be opposed to the stator electrode via the stator.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the detailed description of preferred embodiments thereof with reference to the drawings.